Modular Approach to Tridentate N,O,N′ Ligands Using Pyrazolylborate Chemistry

Two anionic tridentate N,O,N′ chelators, [pz(Ph)B(μ‐pz)(μ‐O)B(Ph)pz] − ( 3 − ) and [pz Ph (Ph)B(μ‐pz)(μ‐O)B(Ph)pz Ph ] − ( 4 − ), as well as the corresponding complexes [Fe( 3 )(py)Cl], [Fe( 3 )Cl 2 ] and [Cu( 3 )Cl], have been synthesised and structurally characterised by X‐ray crystallography (pz: pyrazolyl, pz Ph : 3‐phenylpyrazolyl, py: pyridine). Since our synthesis approach takes advantage of the highly modular pyrazolylborate chemistry, inexpensive and relatively resistant N,O,N′ ligands of varying steric demand are readily accessible. The complexes [Fe( 3 )(py)Cl] and [Fe( 3 )Cl 2 ] possess a distorted trigonal‐bipyramidal configuration with the pyrazolyl rings occupying equatorial positions and the oxygen donor being located at an apical position. The complex [Cu( 3 )Cl] crystallises as chloro‐bridged dimers featuring Cu II ions with ligand environments that are intermediate between a square‐planar and a trigonal‐bipyramidal geometry.